Some telephone handsets are used in a so-called handset mode, wherein they are placed close to the face of a user with the receiver portion placed against an ear, and in a loudspeaking mode, wherein they are located a distance from the face of the user. Loudspeaking mode is often used in applications requiring that the handset be held in one hand and dialed, while the user listens to voice responses, where there is a display on the handset, etc.
In order to provide a loudspeaking mode, handsets have typically used two transducers facing opposite directions (i.e. with a receiver facing the front and a loudspeaker facing the rear of the handset), or facing the same direction (i.e. the front of the handset) but located at the top and bottom of the handset.
In the first case, the loudspeaking audio quality can be compromised due to audio diffraction around the handset. To obtain optimal audio quality the user must rotate the handset so that the loudspeaker faces the user, which places the dialing keys and display (if one were used) in an inconvenient position. Further, while the receiver provides reasonable audio quality when used in the handset mode when the handset is sealed around the ear of the user, it provides relatively poor audio quality (losing low frequencies) if it is not sealed around the ear of the user, for example if the user is wearing earrings.
In the second case, separate microphones must be used for the handset and loudspeaking modes, to maintain acoustic stability, which incurs cost. This solution also suffers from loss of low frequencies in the case that the handset is not sealed to the ear of the user, in the handset mode.